Radio transmitting system



May 13, 1930 ANDREWS 1,758,816

RADIO TRANSMITTING SYSTEM Filed June 5, 1929 Inventor: Paui DA ndre UUS, 1 by m I His Attorney- Patented May 313, 1931i) cairn ras attain FFlC PAUL D. ANDREWS, OF SCHENEC'IADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK RADIO TRANSMITTING SYSTEM Application filed June 5, 1929. Serial No. 368,669.

My invention relates to radio transmitting systems, and more particularly to means for exciting radiating antennae.

It has for one of its objects to provide means wherebyan antenna having certain physical characteristics may be efliciently operated over a very broad range of fre' quencies.

A further object of the invention is to provide a tuning means including a mutual coupling between the antenna circuit and the exciting source of-oscillations together with switching means of simple construction whereby the antenna may be caused to operate efiiciently over a wide range of frequencies. On page 758 of the book entitled Princlples of Radio Communication, first edition,

} by J. H. Morecroft, published by John Wiley and Sons, of New York, is shown a curve representing the general frequency-reactance characteristic of a vertical antenna. It is apparent from this curve that at a certain low fundamental or natural frequency of the antenna the reactance of the antenna is zero' and that the reactance is zero at each of the odd harmonics of this frequency. This curve further shows that at the even harmonics of this frequency the reactance is infinite and that as the frequency increases from one of ,these points of infinite reactance the re-.

actance becomes diminishingly capacitive until a frequency corresponding to an odd harmonic of v the fundamental frequency is I reached when the reactance is zero. Beyond this point the reacta-nce becomes increasingly inductive until the next higher even har monic is reached when the antenna again has infinite reactance. v

. Among the objects of my present invention is to provide an arrangement whereby the antenna may be caused to operate satisfactorily over the broadest possible range of frequencies between those frequencies atwhich the reactance is infinite. In this way the antenna maybe made to'operate at practically any frequency higher than the natural period of the antenna with the exception of those frequencies in the immediate neighborhood of the frequencies at which infinite rcactance occurs. I

The novel features which I believe to be characteristic of my invention are set forth with particularity in the'appended claims. My invention itself however bothas to its organization and method. of operation, to-

' gether with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents one embodiment of my invention, and Fig. Q-represents a.modi- 'fication thereof.

Referring to Fig. 1 of the drawing I have shown at 1 a source of high frequency oscillations of variable frequency which is associated with a radiating antenna. 2. As shown in the drawing oscillations from the source 1 are supplied to the control grid of an electron discharge amplifier 3, where they are amplified and sup-plied to an output circuit which includes the resonant circuit 4. High frequency oscillations set up in the resonant circuit 4 are supplied to the antenna 2 through a coupling condenser 5 and switch 6 arranged between the coupling condenser and the antenna. The antenna is connected directly to stationary contacts 7 and 9 on the switch and through a variable tuning condenser 10 to an additional stationary contact 8 on the switch. The movable element of the switch 6 is arranged to engage in its different positions each of the contacts 7, 8 and 9, andsimuh ,taneously to engage with additional contacts any desired frequency within a fairly broad The inductance 14 then constitutesrange. a mutual coupling between the resonant cirmadecuit including the antenna and that" comprised in the output circuit of the amplifier 3, the cathode of the amplifier being connected to ground at 15. Preferablythe condenser is so'adjustedthat the reactance of the antenna together with the condenser 10 1s capacitive over a large portion of the range of frequencies between points "of infinite reactance of the antenna. The condenser is 10 then fixed in position and tuning within this range is effected by the inductance 14.

This manner of adjustment simplifies the tuning operation, requiring only one main tuning c0ntrol. By turning the switch 6 to -engage contacts 7' and 11 the condenser 10- tions in current rather than in voltage, that is at a nodal voltage point, this point being ,30 directly between the inductive and capacitive react-ance of the reasonant circuit comprising the antenna.

Over a. certain range of frequencies approaching those frequencies at which the re-' actance is infinite, tuning of the antenna by means of inductance and capacity .can not readily be effected and accordingly current feeding of the antenna as above indicated is not practical. -In order to operate the antenna 40 over these frequencies the switch 6 should be turned to engage its contact 9. In this position the antenna is connected directly through the coupling condenser 5 to the resonant circuit 4 and the mutual coupling or tuning coil 14: is eliminated from the circuit. In this way the entire voltage variation of the resonant circuit 4 is supplied directly to the antenna through the coupling condenser 5. Since, due to the high impedance of the antenna very little currentflows in the condenser 5, practic-ally the entire output voltage is impressed upon the antenna. Thus in this position of the switch the antenna is principally voltage fed, or is fed near a nodal current point of the antenna circuit.

' q The arrangement shown in Fig. 2 difiers I from that shown in Fig. 1 in that the antenna is connected directly to all of the upper contacts of the switch. Of course the antenna 0 may be connected directly to the armature of frequencies where the antenna reactance is capacitive the switch 6 will be placed in engagement with contact 11 and tuning will be effected bythe inductance 4 which also serves as mutual inductance between the resonant inductance 4 and the antenna circuit. In that range of frequencies where the antenna reactance is inductive the switch will be placed in engagement with the contact 12, and the mutual coupling will then be capacitive. In the extreme portions of either of these ranges of frequencies approaching the frequency at which the impedance of the antenna is infinite, the switch will be placed in engagement with contact 9, whereby the antenna may be voltage fed.

It will thus be apparent that I have provided a Very simple switching and tuning arrangement whereby the antenna may be ad justed to operate at practically any frequency in the radio range greater than the natural period of the antenna.

While I- have shown particular embodiments of my invention, it'will of course be apparent that certain modifications will readily suggest themselves to persons skilled in the art, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim-as new and desire to secure by Letters Patent of the United States, is:

1. In combination, anantenna, a source of oscillations of frequency variable over a wide range, said source having a ground connection, a connection between said source and said antenna, coupling means connected between said connection and ground, said conpling means being variable substantially to resonate with the.impedance of said antenna over a range of frequencies, whereby said antenna is prlncipallycurrent fed from said source over said range of frequencies and switching means arranged to interru t the connection of said-antenna with sai coupling means and make another connection whereby said antenna is princi allytvoltage fed from said sourceat other requencies.

2 In combinatien an antenna, a source of oscillations of freque cy variable overa wide range, a plurality of impedances including inductive rcactance and capacitive reactance connected inseries between said antenna and ground, switching means included in the connection between said impedances having an element'movable through a plurality of positions, and a connection between said element and ground including said source, said switching means being arranged in one position. thereof to connect said antenna directly through one of said impedances to ground and in another position thereof to connect said antenna to said source and when in said position to interrupt said connection to ground through said last mentioned impedance.

3. In combination, an antenna, a source of oscillations of frequency variable over a broadrange, said source having an output resonant circuit connected to ground, an additional resonant circuit including said antenna. and a variable reactive impedance connected between said antenna and ground, a coupling condenser connected between said first mentioned resonant circuit and said reactive impedance and antenna, said reactive impedance constituting a mutual coupling between said resonant circuits, and switching means for interrupting the connection of said antenna to said reactive impedance while maintaining the connection of said an tenna to said coupling condenser whereby said antenna is subject to practically the entire voltage variation of said first mentioned resonant circuit.-

In witness whereof, I have hereunto set my hand this 4th day of June, 1929.

PAUL D. ANDREWS. 

